Much is at stake for McNeil and its parent company. Johnson & Johnson does not report sales of Tylenol, but total sales of all over-the-counter medicines containing acetaminophen were more than $1.75 billion last year, according to Information Resources Inc., a retail data service.
Safety experts are most concerned about "extra-strength" versions of Tylenol and other pain relievers with acetaminophen found in drugstores. A typical two-pill dose of Extra Strength Tylenol contains 1,000 milligrams of acetaminophen, compared with 650 milligrams for regular strength. Extra Strength Tylenol is so popular that some pharmacies don't even stock regular strength.
Most experts agree that acetaminophen is safe when used as directed, which generally means taking 4,000 milligrams, or eight pills of Extra Strength Tylenol or less, a day.
Each year, some 100 million Americans use acetaminophen, but liver damage occurs in only a fraction of 1 percent of users. Still, liver specialists say those cases are preventable. Part of the problem, they say, is that there are sometimes hundreds of pills in a bottle, making it easy for consumers to pop as many as they please. For example, McNeil sells Extra Strength Tylenol in bottles containing up to 325 tablets
"The argument goes that if you take acetaminophen correctly you will virtually never get into trouble," says Dr. William Lee of the UT Southwestern Medical Center, who has studied acetaminophen toxicity for four decades. "But it's the very fact that it's easily accessible over-the-counter in bottles of 300 pills or more that puts people in harm's way."
Lee applauded the new warning, but said McNeil's marketing has contributed to the "freewheeling" way that Americans take the drug. For decades, McNeil has advertised Tylenol as "the safest kind of pain reliever" when used as directed. "That has been their standard ploy in the past, and I would argue that safest it is not," he says.